1. Field of the Invention
The present invention relates to production method and mechanism for the production of bituminous hot mix (asphalt) in plants where aggregate and micro granulated dust particles obtained from ballast material are used as raw material and collected within a closed system. In this system, aggregate materials are crushed and separated through to screens considering the requirement for their relative particle sizes and grades and deposited. Later aggregates are either transferred into the asphalt plant for continuous feeding of the system or taken directly for discharge.
2. Description of Prior Art Including Information
In order for better understanding of present invention, terms and definitions characteristic to this technical field are explained below:
Aggregate: Main raw material used in asphalt production, obtained through crushing of hard stone particles.
Bitumen: raw material obtained from petroleum, used to attach aggregates to each other.
Crusher Plant: Plant for crushing and sieving hard stone particles.
Asphalt Plant: Plant for asphalt production.
Asphalt: Material obtained from mixing of aggregate with bitumen, used especially for paving of roads and open spaces.
Gradation: Relative size of a stone particle in a graded series.
Ballast: Stone particles with 25–65 mm in size, they are crushed in primary crusher after extracted from stone quarry to be separated from other foreign particles.
Asphalt is obtained through several steps which involve the mixing of hot bitumen with specified sized of aggregates collected together according to their sizes and heated in controlled manner.
In FIG. 1, hard stones used in asphalt production are shown. They are obtained through dynamiting stone quarries, mines or river beads and transferred into crusher to unit. This material usually contains soil and large, coarse stone particles which are crushed with various crushing elements such as jaw crusher, impact crusher, hammer crusher etc. at two stages known as primary crushing and secondary crushing. This is shown in FIG. 2.
In order to produce aggregate, first soil material inside the crushed stone particles are roughly eliminated through by-pass system later coarse stone particles go through crushing and sieving stages to produce aggregates at required sizes in crushing units which are arranged in horizontal fashion.
As it is seen in FIG. 2, crushing procedure is carried out at two sequential orders called primary crushing stage and secondary crushing stage. Transport and conveyance between these two stages are made with conveyors.
Large stone particles are almost reduced less than 150 mm in size in primary crushing whereas a further reduction in size which is almost less than 25 mm is get through secondary crushing.
Crushed stones (aggregates) are classified according to their sizes by passing through screens at various sizes (FIG. 2) and these classified aggregates (for example classified between 0–4 mm, 4–7 mm, 7–12 mm and 12–19 mm) are stored at open areas as shown in FIG. 3 without allowing them to mix with each other. Each category of classified aggregates is then transferred to cold aggregate bunkers to be used as raw material for asphalt production. This is shown in FIG. 4.
Aggregates are transferred into conveyors (FIG. 4) via passing through feeders placed under bunkers and discharged into drying oven where aggregates are advanced inside the oven by a rotating motion and dried with the help of hot air and heated inner surface of dryer oven as a result of vaporization of water vapor inside aggregates. Temperature inside dryer is raised up to 160 C. Drying ovens are generally heated with burners which consumes fuel either in liquid or in gas forms. (FIG. 4)
Burned gases from drying oven are thrown out usually with an exhaust pipe after they have been initially treated with a high capacity dust retaining filter placed above the plant's exhaust system in order to prevent;                1. environmental pollution which is caused as a result of mixing and spreading of micro granulated dust particles inside aggregate and burned air inside dryer oven with water vapor and exhaust gases during emptying from pipe,        2. escape of dust particles which are important raw material for good quality asphalt production and to store them        
Dust particles are retained in cyclones of this filter system to be used as filler material. As shown in FIG. 4, this application is started to be widely used except some plant types.
Filler material collected in cyclone units are transferred into filler silo through the use of spiral conveyor (FIG. 4).
Aggregates heated and dried in dryer oven are transferred into asphalt plant through vertical elevator (FIG. 4). As it is seen in the figure, hot aggregates are passed through with multi-layered screen unit for further screening, classified according to their sizes and discharged into hot aggregate bunker.
Aggregates required for asphalt production at certain quantity and sizes are weighed automatically and transferred into mixer.
On the other side, bitumen which will also be used in asphalt production are automatically weighed in bitumen weighbridge and added into aggregate content inside the mixer.
Now, aggregates and bitumen which come together inside the mixer are thoroughly mixed during a definite time interval to obtain a homogenous bituminous hot mixture (FIG. 4).
Mixture obtained through this process are either directly discharged over carrying vehicle or stored in ready asphalt bunkers before carrying for use.